The best thing I learned is that there are just two words — count ’em! — in English that use “w” as a vowel. Both are loan words from Welsh, no language for those who fear consonants. They are cwm, rhymes with “tomb”, meaning a cirque — a feature formed at the leading edge of a glacier; and crwth, a Welsh lyre, rhymes with “tooth.”

As the Wikipedia entry solemnly points out, that suggests that the correct pronounciation of pwn is “poon,” as in Jonah just got ‘pooned.

Maybe you all knew that, but I am greatly relieved to have that settled.
Even better — there’s a sort onomotopeia going here. That pronounciation just sounds right for the meaning…and it has a nice echo from the use of the word for all sorts of misbehaviour going on in Neal Stephenson’s ur-Cyberspace text, Snow Crash.